In a case of using, in particular, a large iron core in a stationary induction apparatus configured with the iron core including an iron core leg part and an iron core yoke part, and a plurality of windings wound around the iron core leg part, then the iron core is clamped by upper and lower iron core clamps from both sides in a lamination thickness direction of the iron core, an iron core shape is firmly held, and the windings are held using the clamps.
Furthermore, it is known that the leakage flux generated from the windings in a case of driving the stationary induction apparatus may be a cause for a loss of an internal structure of the stationary induction apparatus or generation of electromagnetic-mechanical forces generated in the windings. Specifically, since much of the leakage flux from the windings diffuses into a space and enters the upper and lower iron core clamps before arrival at the iron core yoke part, eddy currents are generated in the clamps, resulting in the loss.
As one of methods of overcoming this problem, Japanese Patent Laid-Open No. 1990-148811 discloses a structure for installing a single magnetic material ring in each of upper and lower sides of a plurality of windings wound around an iron core leg part. There is shown that with using this configuration, magnetic flux leaking from end portions of the windings is absorbed by the magnetic material rings before diffusion into a space, and thereafter, the leakage flux flows within the magnetic material rings in an incident angle direction and arrives at an iron core yoke part before arrival at the clamps, so that effects of suppressing the generation of eddy currents in iron core clamps and reducing a loss are produced.
Meanwhile, in order for reducing generation of electromagnetic-mechanical forces generated in windings due to leakage flux, Japanese Patent Publication No. 1978-25092 proposes a structure that disc-shaped laminated magnetic materials having different radii are independently installed in respective end portions of a low-voltage winding and a high-voltage winding at one magnetic leg. With using this configuration, magnetic flux leaking from the end portions of the windings is absorbed by the magnetic material rings before diffusion into a space and arrives at an iron core yoke part; thus, magnetic flux distributions in the end portions of the winding change. Therefore, there is disclosed that the electromagnetic-mechanical forces are reduced, compared with a case in which the magnetic material rings are not Provided. There is also disclosed that preferred insulation properties can be obtained since the respective magnetic material rings are independently disposed in the end portions of the low-voltage winding and those of the high-voltage winding.